:root {
    --background-color: #2c3e50;
    --border-color: #7591AD;
    --text-color: #34495e;
    --color1: #EC3E27;
    --color2: #fd79a8;
    --color3: #0984e3;
    --color4: #00b894;
    --color5: #fdcb6e;
    --color6: #e056fd;
    --color7: #F97F51;
    --color8: #BDC581;
    /* 这里也是定义的变量--开始的 */
}

* {
    margin: 0;
    padding: 0;
}

html {
    font-size: 14px;
}

body {
    width: 100vw;
    height: 100vh;
    background-color: var(--background-color);
    display: flex;
    justify-content: center;
    align-items: center;
    font-family: 'Montserrat', sans-serif, Arial, 'Microsoft Yahei';
}

.box {
    position: relative;
    width: 400px;
    height: 400px;
    /* background-color: lawngreen; */
    display: flex;
    justify-content: center;
    align-items: center;
}

.box span {
    position: absolute;
    border: 1px solid #fff;
    box-sizing: border-box;
    border-radius: 100%;
    animation: animate 3s linear infinite;
    animation-delay: calc(0.5s * var(--i));

}

@keyframes animate {
    0% {
        width: 0;
        height: 0;
        opacity: 1;
    }
    50% {
        opacity: 1;
    }
    100% {
        width: 400px;
        height: 400px;
        opacity: 0;
    }
}